Our aim is to study the distribution of nicotinic acetylcholine receptors in intact and cultured tissues of the peripheral and central nervous system in relationship to the development and function of synapses. To this purpose histochemical localization of alpha-bungarotoxin bound to the receptors is used in conjunction with light and electron microscopy. In the past year we have continued our study of the formation of cholinergic synapses in developing chick retina, using an alpha-bungartoxin-horseradish peroxidase conjugate; we have extended our studies on the control of nicotinic acetylcholine receptor aggregation on cultured skeletal muscle cells by macromolecular factors secreted by neuroblastoma-glioma hybrid cells and embryonic neurons; and we have initiated work on the structural interaction between the cytoskeleton and nicotinic acetylcholine receptors in cultured skeletal muscle cells.